1. Field of the Invention
The present invention relates to drill bits used in the oil and gas industry. Specifically, the invention relates to an improved method of manufacturing earth-boring bits for drilling earth formations.
2. Background Art
Drill bits are used in the oil and gas industry to drill earth formations in the exploration for gas and oil. FIG. 1 shows a drilling rig which incorporates a drill bit 101. Drill bit 101 is connected to the bottom of a drill string 103 to drill a wellbore 105. The drill string is controlled by surface equipment configured to rotate the drill string, apply downward force to the drill bit to penetrate the earth formation (referred to as weight on bit (“WOB”)), and supply drilling fluid to drill bit 101 by pumping the fluid through a bore of the drill string. Because a variety of earth formations are penetrated in the pursuit of oil and gas, several different types and configurations of drill bits are used. These drill bits are usually grouped into two different categories, shear cutter bits and roller cone bits.
Shear bits are drill bits that cut the earth's formation by primarily scraping the earth formation when drilling. The shear bit is fixed to the drill string which is rotated so, as the drill string rotates, the bit also rotates to cut into the earth formation. The shear bit has a plurality of cutting elements arranged on the body of the drill bit such that the cutting elements scrape and shear the earth formation from the bottom and sides of the wellbore as the drill bit is rotated. Shear bits do not have any moving parts upon the bit itself, only the bit body moves from the rotation of the drill string.
Roller cone bits, in contrast, are drill bits having cones rotatably mounted onto journals. The roller cone bit typically has a bit body with at least one journal, in which a cone is mounted thereupon and allowed to rotate. As the bit body is rotated by the drill string, the cones rotatably contact the earth's formation. A plurality of cutting elements arranged on the roller cones crush and scrape the earth's formation as the bit is rotated. Even though both types of drill bits are useful for drilling into earth formations, only shear bits will be discussed from this point forward.
Shear bits can be further grouped into two categories: steel body bits and matrix body bits. Steel body bits typically have their heads machined from solid pieces of metal, typically steel. Upon completion of the machining, the remainder of the steel body bit is assembled with a bit shank. Usually shear bits use polycrystalline diamond compact (“PDC”) cutters or some other type of wear resistant material to shear the earth formation.
In contrast, matrix body bits are constructed using a powder metallurgy manufacturing process. A cutter head mold of the desired bit head shape is constructed and filled with matrix powder and a binder. Next, the mold is placed in a furnace to allow the binder to melt and infiltrate the matrix powder. As the binder infiltrates the matrix powder, a solid metal casting is formed. The two general types of matrix body bits consists of bits which incorporate PDC cutters for cutting elements, and bits which incorporate natural diamonds impregnated in the matrix powder to shear the formation. In addition, bits may be manufactured with combinations of the two matrix bit body technologies. The focus of the remaining discussion will be directed toward matrix body bits.
Typically, the mold from the matrix body bits defines the external geometry of the bit head, as well as the internal hydraulic passageways. The external geometry of the mold defines the blade shape and junk slots of the bit head, the receptacles for cutters on the blades and on the blade body, and the drilling fluid nozzle orifices. The internal hydraulic passageways of the matrix body bit usually include nozzle ports and an internal fluid plenum. The internal hydraulic passageways of the matrix body bit are used to distribute the drilling fluid pumped through the drill string to various orifices on the face of the bit head. The plenum is generally defined as the internal volume from which all of the nozzle ports receive drilling fluid. The drilling fluid helps cool and clean the bit head, and also carries the cuttings away from the wellbore and back up to the surface.
Before the sintering process in manufacturing the matrix body bits, nozzle displacements and an internal plenum blank are set within the mold of the matrix body bit to form the internal hydraulic passageways. An internal plenum blank defines the internal plenum of the internal hydraulic passageways, and the nozzle displacements define the nozzle ports that will act as receptacles for the nozzles to be assembled with the bit later. Alternatively, the ports defined by the displacements are mere orifices through which the hydraulic fluid travels without the subsequent installation of nozzles. Nonetheless, the nozzle displacements are installed into the mold of the bit head and machined to create a plane, commonly referred to as an “interface plane”, which is typically perpendicular to the bit centerline. The internal plenum blank is then installed at the interface plane to be adjacent to the nozzle displacements. The nozzle displacements are typically manufactured of graphite or cast sand, and the internal plenum blank is typically created as a sand casting. As expected, the plenum blank and the nozzle displacements are a negative representation of the internal hydraulic passageways within the matrix body bit, wherein the space occupied by the sand castings and graphite represent the volume of the internal plenum and nozzle ports to be created as a void within a sintered matrix body bit. Following the sintering process, the plenum blank and the nozzle displacements are chipped or machined out of the sintered matrix body bit to create this void.
Before the installation of nozzle displacements, the plenum blank is hand shaped from its original cone-shaped sand casting. An example of such a cone-shaped plenum blank 301 is shown in FIG. 2. Plenum blank 301 includes a pin section 303 and a bell section 305, with an interface plane 307 at the bottom of bell section 305. Before plenum blank 301 is shaped, it is positioned on top of the nozzle displacements such that interface planes of plenum blank 301 and the nozzle displacements are in contact. The location and shape of the nozzle displacements are then transferred by hand to the bottom of the plenum blank interface plane. Skilled workers then begin the process of hand shaping the sand cast plenum blank 301, removing material from bell section 305 to create the internal hydraulic passageways of the matrix body bit. An effective plenum blank will allow for drilling fluid to be efficiently transferred from the pin section down to the orifices on the face of the bit head through the nozzle ports.
The hand shaping of plenum blanks in manufacturing matrix bit bodies creates several issues. For instance, the design of the internal plenum and the transition from the internal plenum to the nozzle ports changes from bit to bit. Because the plenum blanks are hand shaped, each and every design for the plenum blanks is unique and subject to the skill level of the worker shaping the blank. The effectiveness of the hand shaped plenum blanks will therefore vary from pattern to pattern and are not repeatable. Additionally, as bit sizes and designs change, specific configurations and geometries of the plenum blank will need to change as well. An internal plenum design for one particular bit may work well, where the same design for another bit may encounter problems that lead to a washout from internal erosion or to a reduced bit life. Thus, even the most experienced and skilled craftsmen need to continuously refine their manufacturing techniques to accommodate the new bit designs.
Furthermore, the process of hand shaping the plenum blanks makes it difficult to identify problems with the internal hydraulic passageways of a particular bit. Designers cannot effectively analyze hand-shaped internal hydraulic passageways of the bit for improvement. As such, the internal plenum and transition areas to the nozzle ports cannot be reconstructed into a computer model for analysis. Therefore, plenum blanks with optimized transitions from the internal plenum to the nozzle ports are difficult to create. Such ineffective designs can easily occur if sufficient care is not taken by the worker to hand shape the transition region of the plenum blank properly.
Although methods for manufacturing matrix body bits have been successful in the prior art, further improvements may still be obtained by improving the repeatability characteristics and designs of the internal hydraulic passageways. In a market that is driven by using a drill bit multiple times, internal erosion can limit revenue by reducing the number of times a drill bit can be used and rebuilt. While PDC cutters can be replaced several times on a drill bit, the internal hydraulic passageways of a drill bit made from matrix powder are difficult to rebuild or replace. Thus, a method of manufacturing that allows a design to be made with repetition is desirable. Additionally, it is desirable for the method to allow a designer or engineer to design the interior components of a bit, analyze the design for improved performance, and manufacture the improved design.